We have developed a model system for exploring how changes in an animal's physical and social environment result in the remodeling of its excitable membranes. The teleost electric fish Brachyhypomus pinnicaudatus produces an electric waveform for electrolocation and communication. Shape and amplitude of the electric waveform are determined by ion conductance and kinetics of excitable membranes in the electric organ. Waveform properties change both gradually (hours- days) and quickly (minutes). These two time courses are consistent with genomic steroid action and a non-genomic action respectively of unidentified hormones working to modify the excitable membranes of the electric organ. We can elicit changes in the fish's electric waveform properties by manipulating light and social conditions in the lab. In the project proposed, we shall determine which hormones produce the rapid and slow changes we see in the electric waveform and identify the ionic mechanisms underlying the changing waveform. A strength of this system is the scope of its biological relevance; we understand the behavioral significance of the electric waveform changes, so by determining the cellular and molecular mechanisms, we can draw a long chain of continuous causal connections, from social behavior to the underlying gene regulation of ion channels and 2nd messenger systems. A potential benefit of this project is the possibility of localizing important new biomolecules including membrane receptors for sex steroids.